Photo-electric photometer



June 5, 1928. 1,672,671

c .1. YOUNG PHOTO ELECTRI C PHOTOMETER Filed Jan. 20, 1927 AMFLFIER' Patented dune 5, l92i8. p.

i 1,672,671 unirse srATEsPAT'ENT oFFicE.

CHARLES l', YOUNG, OF SCHIENECTADY, NEW YORK, ASSIGNOR T0 GEv-N'ERAL EECTBIG confirm, A CORPORATION or Nnw YORK.

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-Application led January 20, 1927. Serial No. 162,405.

My present invention relates to an arrangement for comparing the illuminating power of a plurality of beams of light.

lt is one o the objects of my invention to provide a system employing a light sensitive cell for edecting anaccuratecomparison of the illuminating power of a plurality of heams of light which shall be independent 'through the cell proportional to the illuminating power of each heam. Each light loeam is periodicaldy interrupted, the numher or interruptions ci one beam in a given time being greater than -the number or inf terruptions oi another beam in the same time. The currents thus produced in the light sensitive cell control the potential of the-'control elementuof an electron discharge 'i device and produce a current in the output circuit thereof composed oil components having frequencies proportional to the number oi? interruptions oi each light beam. This current is supplied to circuits resonant at the frequencies oit the components and controlling Aan indicating device., D

lhe novel teatureswhich lloelieve to. be characteristic ci niyinvention are set iorth with particularityin the appended claims. My invention itself2 however, vvill best be` understood trom reierence to the following speciiication when considered in connection with the accompanying drawing in which the single ligure represents orashows dia-5 grammaticelly a circuit organization and arrangement oil parts whereby my invention may be carried into odset. v

Vlleterring tov the drawing, l have indicated at l, a boa or container within which is mounted a shaft 2v driven hy a motor 3 of any suitable type and reasonably constant speelt` Shaft 2' carries at one end thereotQ 'y inner concentric ring o, t e number of holes in the outer ring being considerably greater and adjacent a side of the container 'a circular perforated dish el. Dish e is provided with an cuter ring ci h les 5 and with aliy than the number oil holes 7m the inner ring., Two. light sources, one of which 7 may be talren as a standard and the other 8 as a.

`variable source, are mounted on the outside of box 1. Light from source 7V is directed through alens 9, an openin 10, and the inner ring vholes 6 on to a re ecting mirror 1l and then through lens 12 upon the light sensitive cell 13 which in the present instance is a photo-electric cell. the source 8 is directed through a lens let,l opening l5 and the openings of ring 5 on to a reflecting mirror 16 and then through a lens 17 on to the light sensitive cell.

Cell 13 is connected tothe control element 18 ofen electron discharge device 19 which is used as an amplifier. A potential is normally impressed on the cellthrough a re-A sistor 20 by a source of energy 21. The control element is normally negative but as light Light from" is directed onto the cell 13 and current flows through the cell and resistory 20 the negative charge on control element 18 is reduced, and

increased current flows in the output circuit ci the discharge device. This output circuit is connected to an amplier 22 which excites a pair of circuits 24,3 and 24 tuned' to be resonant at certain frequencies.

lleater elements 25 and 26 are connected ink circuits 23 and 24 respectively andX are adapted to heat a pair ofthermo-electric couples 27 and28 which are connected in opposition to one another and in circuit with anindicator or meter 29., A

ln the operation of the device shown, when dish l is rotated7 the light beam from source 7 is -interrupted periodically about Jdve hundred times per second and that .from source 8 about nine hundred times per second. The variations in the potential of the grid 18 produced by the current ilovving through cell 13 cause corresponding variations in the currentl owing in the output circuit'oirthe discharge device.A The form oi the current wave may be controlled by the torni oz? the openings in the disk e or by the form or the openings 10 and 15. ln the present instance the wave fis of complex :toi-in; including a steady component and superimposed on this twovvaves otsubstantially sine term, one having a frequence of tive hundred and the other of nine hun red cycles per second. The tuned circuits 23 end 2dare resonant at frequencies of five hundred cycles and nine hundred cycles per sec ond and when current of these fre uenciee tlows in the tuned 'circuits the heater e ements 25 and 26 are energized. If the amounts of from each light directed on to the light sensitive cell i3 of the sources of light 7 andy 8 are equal, the currents flowing in the heater elements will be equal 4and since the thermoelectric elements are connected in opposition no indication will be registered on the indicating device 29. llf, however, the amounts of light directed on to the light sensitive cell are unequal, elements 25 and 26 will be heated unequally, the thermoelectric junctions will be heated unequally, and the pointer assciated with the indicating device will be moved to the right or left to give an indication of the relative intensity of theftwo light sources. lf the variations of current flowing in the output circuit of the discharge device are relatively large the portions of the circuit included between the dotted lines 1v-a and b-Z) may be omitted if desired and the current supplied directly to the tuned circuits 23 and 24: rather than to an amplifier.

When the light densities of two samples of material are to be compared the light vsources l and 8 are replaced by these samples and the samples illuminated from an.- other and preferably a single source of illumination. 'lhe operation of the remainder of the equipment is the same as described above. lt is obvious that the ability of tvvo samples to reflect light can be compared in an analogous manner and with no alteration in the principle employed.

W hat ll claim as new and desire to secure by Letters Patent of the United States is l. rll`he combination in a system for com paring the illuminating power of diderent light beams, of a light sensitive cell, means for directing the light beamson to said cell, means for periodically interrupting one light beam at a predetermined frequency, means for periodically interrupting another light beam at a diderent predetermined frequency,v

and means for comparing the intensity of the current produced in the cell by one light beam with the intensity of the current produced in the cell by another light beam.

2. .The combination in a system for comparin c the illuminating power of different light, cams, of a light sensitive cell, means vfor directing the light beams on to said cell,

means forI periodically interrupting one light beam at a; predetermined frequency, means for periodically interrupting another light beam at a different predetermined frequency, and means for comparing the intensity of the cur/rent produced in the cell by one light beam with the intensity of the current produced in the cell by another light beam, said means comprising a plurality of tuned cir` y cuits connected to the light sensitive cell.

3. The combination in a system for comparin the illuminating power of different light earns, of a light sensitive cell, means for directing the light beams on to said cell,

nevacvi means for periodically interruptingione light beam at a predetermined frequency, means for periodically interrupting another light4 prising an electron discharge device having f an output circuit and a control element, a single light sensitive cell connected to the control 'element and adapted to receive light from said sources, means for periodically interrupting the light from each source to thereby vary the potential of said control element, the number of interruptions of the light from/ one source being greater than the number of interruptions of the light from the other source to thereby produce a current in said output circuit having coinponents of dierent frequencies, a plurality ofcircui'ts resonant to said frequencies, and means responsive to the current in said circuits for controlling an indicating device.

5. ln combination, a plurality of light sources, means for comparing the illuminating power ofsaid sources, said means comprising an electron discharge device having an output circuit and a control element, a single light sensitive cell connected to the control elementkand adapted to receive light from said sources, means for periodically interrupting the light from each 'of said sources to thereby vary the potential of said control element, the number of interruptions of the light from one source being greater than the number of interruptions of the light from the other source to thereby produce a current in said output circuit having components of dierent frequencies, a plurality of circuits resonant to said frequencies, a pair ofthermoelectric junctions oppositely connected to an indicating element, and heating elements connected in each of said resonant circuits and adapted to control the operation of said thermoelectric junctions.

j 6. ln' combination, an electron discharge device having an output circuit and a control electrode, a light sensitive cell connected to the control electrode, means for directing a will) ias said current comprising two comcuits and resonant to said frequencies, and an indicating device responsive to current HOW- ing in said resonant circuits.

7. `rihe method of comparing the illuminating power of different light beams which comprises generating an electromotive force comprising components of different frequencies, each component having a value proportional to the illuminating power of one beam,

supplying said electromotive force to cirl@ n witness whereof, I have hereunto set 15 my hand this 18th day of January, 1927.

CHARLES J. YOUNG. 

